1. Field of the Invention
The present invention relates to ingredients for use in pyrotechnic gas generant compositions, and more specifically to fuels containing a high oxygen balance. The gas generant compositions are useful as gas generant propellants for air bag occupant restraint systems for automobiles, gun propellants, inflation and expulsion devices, flotation devices, ignition materials, pyrotechnics, fire suppression devices and smokeless and smoke producing rocket propellants.
2. Background Art
There is high demand for pyrotechnic gas generant compositions which on combustion yield acceptable burning rates and provide, at relatively low flame temperatures, a high volume of substantially non-toxic gas and a low volume of solid particulate matter that can produce smoke. It is also important that resulting solid by-products from the combustion of gas generant compositions be minimal, and the gaseous combustion products be substantially non-toxic, and non-corrosive. Various compositions of gas generants have been utilized in the past in an attempt to reach the above desirable characteristics.
U.S. Pat. No. 3,405,144 discloses a 1-azido-N,N,Nxe2x80x2-trifluoroformamidine that is useful in a propellant composition which exhibits a high specific impulse. Specifically, the said material is disclosed to be useful in rocket fuel compositions.
Gas generant compositions have also been developed to include the addition of modifiers to lower flame temperatures and increase gas production. Further ingredients may be added such as binders, ignition aids, slag formers, scavengers, and catalysts to improve various features of the underlying propellant. The modifiers and additional ingredients often times, however, improve one aspect of the propellant composition while also contributing to the production of undesirable by-products and may increase the corrosiveness thereof. This is particularly disadvantageous in an automobile air bag environment.
One major gas generating composition having desirable characteristics contains strontium nitrate and 5-aminotetrazole (SrN/5ATZ) as major constituents. This formulation is relatively non-toxic when compared with sodium azide systems, has good ballistic properties and retains the majority of solid combustion products as a slag or clinker either in the combustion or filtration areas of, for instance, an air bag system for an automobile. These formulations also exhibit acceptable flame temperatures of 2250xc2x0 K. to 2750xc2x0 K. depending upon the stoichiometry of the formulation and the oxygen to fuel ratio. Moreover, the strontium nitrate and 5-aminotetrazole formulations are relatively non-hygroscopic and the ingredients do not exhibit crystalline phase changes over the operating temperature range of the air bag system.
Such a formulation, however, suffers with regard to gas output, specifically, in the volume limited systems of a driver""s side air bag. This is because a high concentration of strontium nitrate is required to maintain a neutral oxygen to fuel (O/F) balance. Because inflator designs are becoming smaller and smaller and, thus, more volume limited, propellants are required to provide greater gas output and still retain the desirable attributes of the strontium nitrate/5-aminotetrazole systems.
Approaches have been taken to obtain the attractive features of the above-noted propellants, while overcoming the low gas output thereof. This has resulted in the development of propellants based on mixtures of potassium perchlorate and oxygenated fuels such as guanidine nitrate and aminoguanidine nitrate. These propellants are also relatively non-hygroscopic, provide excellent gas output, high burning rates and only about two thirds of the solid combustion products of the above-noted strontium nitrate and 5-aminotetrazole based propellants. Unfortunately, the solid combustion products do not form clinkers or slags which deposit in the combustion or filtration area, but instead form very fine particulates in the gas stream which results in a smokey and dirty exhaust.
Smoke or dirty exhaust combustion products are not commercially desirable, particularly, in automobile air bag systems since the production of such product may cause undue anxiety on the part of drivers and passengers involved in an automobile accident in which air bags are deployed. As a result, there is a need for a propellant material or gas generant that exhibits high gas output upon combustion, but does not produce unwanted by-products upon combustion.
The object of the present invention is to improve upon and to overcome the deficiencies of the prior art and to provide a substantially non-hygroscopic, substantially non-toxic gas producing pyrotechnic gas generant composition that upon combustion produces a high gas output and a high burn rate with limited non-gaseous combustion products.
Another object of the present invention is to provide a pyrotechnic gas generant composition including a high oxygen balance fuel, preferably, azodiformamidine dinitrate, that produces the desirable high gas output at a low combustion temperature and reduced non-gaseous combustion products.
Still another object of the present invention is to provide a pyrotechnic gas generant composition including a high oxygen balance fuel, preferably, azodiformamidine dinitrate, with the capability of self-deflagration similar to a solid monopropellant.
Yet another object of the present invention is to provide a pyrotechnic gas generant composition including a high oxygen balance fuel which will auto-ignite in an inflator at acceptable but low enough temperatures to ensure that the inflator only rupture but does not fragment in a bonfire test.
Still another object of the present invention is to provide a gas generating composition capable of producing a substantially high gas output upon combustion for use as an automobile air bag propellant. However, the composition of the present invention may also be employed to inflate such items as an inflatable raft or passenger escape chute of an airplane, as well as for gun propellants, pyrotechnics, ignition mixtures, fire suppression devices and rocket propellants. From a practical standpoint, the composition of the present invention also may include additives heretofore used with other gas generant compositions, such as oxidizers, gas conversion catalysts, ballistic modifiers, slag formers, ignition aids, energetic plasticizers and binders, non-energetic binders, and compounding aids.
The foregoing objects are generally achieved by a pyrotechnic gas generant composition including a high oxygen compound or fuel, preferably, azodiformamidine dinitrate, which is the resulting reaction product of aminoguanidine nitrate and nitric acid prepared with or without the use of potassium permanganate. Specifically, the reaction product is a yellow precipitate that can be ignited and used alone, with no oxidizers or other additives, for very rapid and substantially smokeless self-deflagration or combusted in combination with oxidizers and/or other additives. In each instance, the gas generant composition provides both high gas output and low production of solid decomposition products upon combustion. Further, the precipitate is relatively non-hygroscopic and has a high burn rate. As a result, cartridges used to contain the gas generating composition are not required to withstand the extremely high pressures associated with prior art gas generating compositions, such as ammonium nitrate based compositions, that exhibit the similar low solid combustion product production as the gas generating composition of the present invention, but have low burn rates and are generally hygroscopic.
Based upon the general physical characteristics of the above-noted reaction product of the present invention, the product is believed to be 1,1 xe2x80x2-azodiformamidine dinitrate. However, the pyrotechnic gas generant composition of the present invention is directed separately to both the use of the yellow reaction product of aminoguanidine nitrate and nitric acid and to 1,1xe2x80x2-azodiformamidine dinitrate.
The azodiformamidine dinitrate may also be formed as the reaction product of nitric acid and other aminoguanidine salts, such as aminoguanidine bicarbonate, aminoguanidine sulfate, or any combination thereof. Preferably, the aminoguanidine salt is aminoguanidine bicarbonate. The use of such materials provide a cost effective means of producing the azodiformamidine dinitrate of the present invention.
The gas generant composition of the present invention is generally prepared by the methods heretofore employed for prior art compositions and generally, but not exclusively, involve the dry or wet blending and compaction of the comminuted ingredients selected for combination. In view of the advantageous characteristics of the gas generant composition of the present invention, namely, high gas output, low solid combustion products production and high burn rate, the generant has applications in automobile air bag systems, inflatable rafts or passenger escape chutes, gun propellants, pyrotechnics, ignition mixtures, fire suppression devices and rocket propellants.
For purposes of the present invention, the terms propellant(s) and gas generant(s) are used interchangeably. Also, for the purposes of this invention, the reactions shown are with anhydrous components. The use of non-anhydrous components, however, is also contemplated.